Black nickel finish



' Patented Nov. 12, 194i) nmcxmcknr. FINISH- n mp Bower Knapp, Westfleld, N. 1., assign'or a; The International Nickel Company, Inci, New York, N. Y., a corporation of Delaware No Drawing.

Application November 13, 1939, Serial No. 304,142

23 Claims. (01. 148-6) The present invention relates to chemically produced colored surfaces on articles having a nickel surface, to a bath suitable for the aforeiron and steel articles is described in U. 8. Patsaid purpose and to the products thereof. It'is recognized by those skilled in the art that the coloring of metals is an art. Accordingly it technique is involved in coloring and can only come from actual experience. v

The composition of the metal will aflect greatly the color to be obtained, Non-ferrous alloys high in copper will take on different hues than those low in copper. Copper and alloys rich in copper can be more easily treated than alloys low in copper. It is necessary in some cases in order to obtain a particular shade to copper plate the article before coloring.

In the 1939 edition of Platers Guidebook, G. B. Hogaboom, Jr. and T. H. Chamberlain also imdicate other factors which have heretofore only been determined by experience. Thus on page 46 these authorities state that Solution formulas may be varied and adjusted to suit particular conditions that will produce desired shades of color. Time of immersion and temperature are other variables that are important and usually arrived at by experience. Many beautiful color effects are obtained in a great many instances by varying the procedure and sequence of operations. From the foregoing it will be appreciated that the coloring of metals has not reached that stage ofdevelopment at which-generalizartions might be made or prophecies given disclos ing the manner in which certain color effects on particular metals may be obtained,

'40 In both'the 1938 edition and the 1939 edition of Platers Guidebook, the composition of solutions and the conditions under which the colori'ng of silver, copper, brass, iron and steel is DOS-y sible are given. "Other solutions for the treatment of non-ferrous metals aredescribed in various U. S. Patents such as U. S. Patent Nos; 1,967,715, 2,001,753 and 2,012,697. For example, U. S. Patent No. 1,967,715 describes a solution suitable for depositing a corrosion resistant coataction of organic acids is described in U. 8. Patent No. 2,001,753. The use of acids including oxalic and benzene-anionic acids for the coating I (Platers Guidebook,

of non-ferrousmetals such as lead, tin and cad-' mium, is disclosed, by Tanner and Lodeesen in U. S. Patent No. 2,012,697; The rust-proofing of "ent No. 2,105,672. None .of the foregoing in- 5 formation provides the'solution to the-problem of providing articles in which the major constituent of the surface is nickel with an adherent black or colored coating. Nor am -I aware that anyone has provided the art with a, simplified, 1

accurately controlled process for providing articles having a surface constituted largely of nickel ,with a black or gray decorative and omamental coating on an industrial scale by simple immersion capable of being employed by com- 15 paratively inexperienced operators. i

It is an object of the present invention to provide a process for coloring or blackening nickel surfaces. v

It is another object of the present invention to 20 provide a bath for coating nickel articles with an adherent black or colored ornamental and decorative film and having a bath 'efiiciency indicator included therein. 1

The present invention also contemplates pro-- viding the art with nickel articles having a grayish to blackish surface, or having coatings of such thinness as to display interference phenomena. 4

Other objects and advantages will become 'apparent from the following description.

Broadly stated. the present invention provides a bath and process which even in inexperienced hands provides decorative surfaces on nickel articles. Operators lacking the experience in metal .33

coloring stressed by Hogaboomv may produce highly ornamental coatings on articles having a. nickel surface by taking advantage of the principles of the present invention.

The novel bath provided by the present invenv tion permits the application of reduction and oxidation reactions to the production of the decorative black coatings on articlesconstituted of nickel. It is my opinion at this time that upon subjecting, a nickel article to the action of the" bath prepared in accordance with the principles of the present invention, a reducing condition is produced in the vicinity 0!, 01' at, and close to the surface of the article through the solution 50 of a small amount of nickel from the surface of the article. This reducing condition causes theformation of a black deposit on the surfacev of the article. Simultaneously, it is believed, an oxidation reaction takes place which may be said 66 fate.

persulfate or hydrogen peroxide and amto act as ascavenger and remove inhibiting reaction products. I

I have found that suitable oxidizing agents for the purpose of the present invention are those oxidizing agents which at unit activity have an oxidation-reduction potential more negative thanabout 1.75 volts. During my investigation of the conditions under which articles having a nickel surface could be provided with black or colored films, the action of a number of oxidizing agents was investigated. I found that ,dichromates, chlorates, and permanganates gave unsatisfactory results when used in conjunction with the other components of my bath. On the other hand, hydrogen peroxide and persulfate gave satisfactory results. As those skilled in the art know, the oxidation-reduction potentials of these oxidizing agents are as follows:

Dichromate -1.36 Chlorate 1.45

Permanganate ,-1.67 Hydrogen peroxide"; -1,77 Persulfa'te 2.05

when used in accordance with the principles of the present invention.

In order that those skilled in the art may have a better understanding of the p'rinciplesfof the present invention, the following description is provided for illustrative purposes. I have'found that a bath having an acidity of about pH 1 to pH 2 is necessary for the production of decorative or utilitarian coatings of articles consisting of nickel or surfaced with nickel. In addition it is advantageous to include in the bath material capable of oxidizing at least one product of the reaction. I have found that in a bath such as described more fully hereinafter, both functions can best be fulfilled by'ammonium persulfate or hydrogen peroxide. When the latter is used, the pH changes less with use than where the persul- "fate is employed. To provide a source of sulfur ions, I have found the use of ammonium thiocyanate preferable. It is advantageous to stabilize a bath containing ammonium persulfate by the addition of a sulfate such as sodium sul- However, baths containing only ammomonium thio-cyanate have given satisfactory results.

Other sulfur containing compounds may be substituted as a source of sulfur containing ions for the thio-cyanate. Among the class of sulfur compounds suitable for this purpose are included sulfites, and thio-sulfates soluble in the bath and especially the alkaline salts thereof. A particularadvantage accrues from the use of ammonium thio-cyana'te in that by the use of a'ferric salt. for

example, the sulfate, a visual indicator of the state of the bath is provided. Thus, in a bath containing both thio-cyanate and a ferric salt, the presence of thio-cyanate is clearly indicated by the red color. When the thio-cyanate is in such low concentration as to renderthe bath inefiective,'the red color practically disappears. In the presence of a sulfate such as sodium sulfate, the persulfate is stable practically indeflnitely, when the bath is idle, although itis consumed'during use. However, the thio-cyanate or other source of sulfur ions must be added from time to time as the concentration thereof falls below practical values. When a solution containing persulfate, thio-cyanate, alkali sulfate and a, ferric salt is a deep red color, deep black finishes may be produced on nickel by a five minute immersion therein at room temperature. As the film forms, a series of colors is produced by interference effect-those of the second order being particularly attractive. When these interference colors rather than gray or black are desired, it is best to use a bath containing low concentrations of thio-cyanate and/or ammonium persulfate or hydrogen peroxide, as such a bath 'cyanate is added from time to time in such amounts as to maintain the red color of the bath.

A bath which I have foundto give very satisfactory black finishes in about 5 minutes has the following composition:

Ammonium persulfate 200 gr/L Sodium sulfate gr/L Ferric sulfate 10 gr/L 'gr/L=grams per liter. To the foregoing bath ammonium thio-cyanate is added from time to time in amounts sufiicient to maintain a deep red color.

I have found that a bath for producing black or colored finishes on nickel surfaces employing hydrogen peroxide as the oxidizing agent has several advantages over a persulfate bath. First. it simplifies the bath by reducing the number of components therein, second, the pH of the bath may be more readily controlled. In this connection, it is of interest to note that while the persulfate bath tends to become more acidic during use, the hydrogen peroxide bath becomes more alkalinewith use.- Accordingly, I maintain the pH of the peroxide bath substantially constant at about 1.2 by the addition of small amounts of sulfuric acid or by the use of a buffer, such as monochloracetic acid, orthophosphoric acid or the like in suitableamounts, for example, about 10 grams per liter.

A bath having the following composition has given satisfactory results:

Potassium sulfocyanate 0.5 gr/L Sulfuric acid 5 gr/L Hydrogen peroxide (30%),. 25 cc pl pH. 1.2

furous and thio-sulfuric to be effective in producing black or colored finishes on-nickel surfaces have beenfound satisfactory. J

While the foregoing baths may be used at about 15 to 20 0., higher bath temperatures be colored black by means of anyof the baths ates, sulfites and thio-sulfates.

may be employed or the article to be treated may be warmed. At higher bath temperatures shorter periods of treatment sumce. However, the lower temperature is to begpreferred, since there is decomposition of the bath at high temperatures.

By'means of these baths and the process of the present invention, the careful control of conditions and the practically continual additions of salts required by the electrolytic processes for producing black nickel are eliminated and 'a simpler and more reproducible method provided.

The process of the present invention is particularly applicable to'the coloring of images on nickel strip or sheet; For this purpose the metal is coated with alight sensitive resist, printed, developed and etched. The etched image can then described hereinbefore. By this means a picture with good contrast and detail is obtained. Thus records can .be made on time resistant nickel film which last indefinitely. The method of the present invention canlikewise be employed for the production of colors other than black for architectural uses. In the formation of the film on nickel a series of interference colors is formed before the film acquires suflicient thickness to be jet black.

Although the present invention has been described in conjunction with certain preferred embodiments, it is to be understood that variations and modifications thereof may be made as those-skilled in the art will readily understand.-

Such variations and modifications are to be considered within the purview of the pre'sentspecification and the scope of the appended claims. Thus, among the alkaline salts which may be employed as sources of sulfur are included ammonium and alkali metal salts of the thio-cyan- Furthermore, the expression, nickel articles as used herein includes articles having a surface possessing a nickel content of at least about I claim:

1. A process for producing decorative, orna-.

mental and utilitarian finishes on nickel and nickel surfaced articles which comprises immersing said articles in a bath having a pH of about 1 to about 2 and containing an oxidizing agent having at unit activity an oxidation-reduc tion potential more negative than about l.'75 volts and ammonium thio-cyanate in effective amounts and subjecting said articles to the action .of said bath at a temperature of about 15" C.

and higher for a period of time up to about 5 minutes. r

2. A process for producing decorative, ornamental and utilitarian finishes on nickel and nickel surfaced articles which comprises subjecting said articles to the action of a bath hav ing a pH of about 1- to about 2 containing an oxidizing agent having at unit activity an oxidation-reduction potential more negative than about .-1. 75 volts and a reducible sulfur compound selected from the group consisting of thio-cyanates, sulfites, and thio-sulfates in effective amounts for a period of time at a temperature of about 15 C. and higher.

3. A process for producing decorative, omamental and utilitarian finishes on nickel surfaced articles which comprises subjecting said articles to the action of a bath containing about 50 to about 200 grams of ammonium persulfate and about 5 grams of ammonium thio-cy'anate perliter at a temperature of atleast 15". C. for a period of time not greater than about 5 minutes.

4. A process for producing decorative, 'omamental and utilitarian finishes on nickel s'ur-" faced articles which comprises establishing a bath containing about 50 to about 200 grams of ammonium persulfate, about 25 to about grams of sodium sulfate and about 1 to about 10 grams of ferric sulfate per liter and at least sufficient ammonium thio-cyanate to produce a red color in said bath, immersing nickel surfaced articles in said bath,maintaining said bath at a. temperature of about 15 C. to about 20 C., subjecting said nickel surfaced articles to the about 5 minutes, and adding ammonium thioaction of said bath for a period of time up to cya'nate at intervals and in quantities suflicient to maintain the red color ofsaid bath.

5. A process for producing decorative, ornamental, and utilitarian finishes on nickel surfaced articles which comprises establishing a bath containing about-50 grams to about 200 grams of ammonium persulfate, a d an effective amount of reducible sulfur compound selected'from the group consisting of sulfates, thio-sulfates and thiocyanates, and an ammonium persulfate stabilizing agent in effective amount, heating said bath to at least 15 C. and subjecting nickel surfaced articles to the-action of said'bath for thereof.

'6. Aprocess for producing decorative, 'ornamental and utilitarian finishes on nickel surfaced articles which comprises establishing a bath containing about 200 grams of ammonium persulfate, about 100 grains of sodium sulfate v a period of time dependent upon the temperature and about 10 grams of ferric sulfate per liter,-

adding at least sufiicient ammonium thio-cyanate to said bath to produce a red color therein and subjecting said nickel surfaced articles to the action of said red .colored bath for a period of time up to about 5 minutes at a temperature of about 15C. to about 20 0.

7.A bath suitable for producing decorative,

' omamental or utilitarian finishes on nickel and nickel surfaced articles which comprises an oxidizing agent having at unit activity an oxidation-reduction potential of at least l .75 volts in effective amounts and a reducible sulfur compound in effective amounts, said bath having a pH of about 1 to about 2.

8. A bath suitable for producing decorative, ornamental or utilitarian finishes -on nickel and nickel surfaced articles and containing an oxidizing agent selected from the group'consis'ting of hydrogen peroxide and ammonium persul fate and a reducible sulfur compound selected from the group consisting of thio-cyanates, sulfites and thio-sulfates, said bath having a pH of about 1 g to about 2.

11. A bath suitable for producing decorative,

ornamental or utilitarian finishes on nickel articles and containing about 50 to about 200 grams of ammonium persulfate per liter, a small but effective amount of a soluble ferric salt and suflicient ammonium thio-cyanate to produce a red color in said bath.

" 12. A bath suitable for producing decorative,

ornamental or utilitarian finishes on nickel arti-' cles and containing about 50 to about 200 grams of ammonium persulfate, about 25 to about 100 grams of sodium sulfate per liter, a small but effective amount to about 10 grams per liter of a soluble ferric salt and at least sufiicient ammonium thio-cyanate to produce a red color in said bath.

13. A bath suitable for producing decorative. ornamental or utilitarian finishes on nickel articles and containing about 50 to about 200 grams of ammonium persulfate and about 1 to about 10 grams of ferric sulfate pe; liter and at least sufflcient ammonium thio-cyanate to produce a red color therein.

14. A bath suitable for producing decorative,.

ornamental or utilitarian finishes on nickel articles and containing about 200 grams of ammonium persulfate, about 100 grams of sodium sulfate and about 10 grams of ferric sulfate per liter and at least 'suflicient ammonium thiocyanate to produce a red color 7 erein.

-15. A bath suitable for producing decorative,-

ornamental or utilitarian finishes on nickel and nickel surfaced articles and containing an effective amount of hydrogen peroxide, a small but efiective amount of a reducible sulfur-containing compound and sufficient of an acid selected from the group consisting of monochloracetic acid, orthophosphoric and sulfuric to produce a pH of about 1 to about 2.

16. A bath suitable for producing decorative, ornamental or utilitarian finishes on nickel and nickel surfaced articles and containing about 0.5 grams per liter of potassium thio-cyanate, about 5.0 grams per liter of sulfuric acid and about 25 cc. of 30% hydrogen peroxide per liter, said bath having a pH of about 1.2.

17. A bath suitable for producing decorative, ornamental or utilitarian finishes on nickel and nickel sinfaced articles and containing an effective amount of a reducible sulfur compound,

about 10 cc. to about 25cc. of 30% hydrogen peroxide per liter and about 10 grams per liter of a butler selected from the group consisting of monochloracetic acid and orthophosphoric acid.

18. A buffered bath suitable for producing dec-- orative, ornamental or utilitarian finishes on nickel and nickel surfaced articles containing effective amounts of hydrogen peroxide and a sulfur compound reducibleat the surface of said articles.

19. A buffered bath having a pH of about 1 to about 2 suitable for producing decorative, ornamental or utilitarian finishes on nickel and nickel surfaced articles containing effective amounts of hydrogen peroxide and a sulfur compound re ducible at the surface of said articles.

20. As a new article of'manufacture, a nickel body having a gray to black finish'produced by simple immersion in a bath containing an oxidizing agent having a negative oxidation-reduction potential of at least 1.75 voltsand a sulfur the second ordenand being produced in a bath containing an oxidizing agent having an oxidation-reduction potential of at least -l.75 vol '5 and a reducible sulfur compound. j

22. A process for producing decorative, or amental and utilitarian finishes on nickel surfaced articles which comprises subjecting nickel surfaced articles to the action of a bath having a pH. of about 1 to about 2 and containing effective amounts of hydrogen peroxide and a sulfur containing compound reducible at said nickel surfaces at a temperature of about 15 C. to about the boiling point of the lath.

23. A process for producing decorative, ornamental and utilitarian finishes on nickel and nickel surfaced articles which comprises subject-- ing such'articles to the action of a bath containing about 10 to about 25 cc. of 30% hydrogen peroxide per liter. about 10 grams per liter of an acid selected from the group consisting of monochloracetic acid, orthophosphoric acid and sul- 

